It is known in the prior art that the corrosion of metals in contact with water or water vapors containing contaminants such as hydrogen sulfide may be inhibited by the addition of certain compositions comprising a low-boiling aliphatic monoamine containing from 1 to 6 carbon atoms either alone or in combination with a salt of a high-boiling aliphatic amine and a carboxylic acid. This inhibitor will prevent the corrosion of ferrous metals which have been exposed to corrosive hydrogen sulfide vapors and also to water which contains hydrogen sulfide. However, as hereinbefore set forth, these corrosion inhibitors are limited to the use of low boiling aliphatic monoamines as the volatile portion of the inhibitor, and to the inhibition of vapor phase and water phase corrosion by hydrogen sulfide.
In contradistinction to this, as will be hereinafter shown in greater detail, the present invention is concerned with a composition which will inhibit the corrosion of metals which are exposed to water or water vapor which contains chloride contaminants. These chloride contaminants are present in crude petroleum fractions and will upon contact with water, at temperatures commonly used in distilling crude petroleum, form hydrochloric acid.
The present invention concerns new corrosion inhibiting agents and especially agents for inhibiting the corrosion which occurs at the top of distillation columns.
It is known that distillation of crude petroleum at atmospheric pressure can be accomplished industrially only if precautions are taken to limit the corrosion of the installations.
Among these precautions, certain measures are taken upstream of the column and others downstream. Measures taken upstream comprise principally desalting of crude petroleum, for example by electrostatic means. The desalting may be followed by a complementary neutralization, for example, by addition of soda.
Measues taken downstream include injection of neutralizing agent in the overhead fraction of the distillation column and injection of corrosion inhibitor.
After desalting and possible complementary neutralization, for example, with soda, the crude petroleum still contains sodium chloride, calcium chloride and magnesium chloride. Unlike sodium chloride, which is stable, calcium chloride and magnesium chloride are hydrolyzed by water vapor at a temperature higher than about 120.degree. C. and thus produce hydrochloric acid. Hydrochloric acid is concentrated in the overhead vapors, and in the water condensed from this vapor.
Crude petroleum, after stabilization, contains practically no dissolved hydrogen sulfide, however, the cracking of sulfur compounds which occurs during distillation, forms hydrogen sulfide, which is also removed overhead in the column.
In order to neutralize the acids present in the overhead vapors, a neutralizing agent, such as ammonia in gaseous phase or aqueous solution, is injected into the line which connects the top of the column to the condenser or into a reflux line at the top of the distillation column. This injection is designed to maintain the pH of the water which condenses in this line at a predetermined value or, more precisely, to keep pH variations within a predetermined range. The pH of this water is closely related to the salts formed in the column overhead vapor line. Thus, effective control of corrosion in the column overhead vapor line depends on close control of the pH of the water that condenses in this line.
A corrosion inhibitor is generally added downstream of the point of injection of the neutralizing agent. This inhibitor forms a film on all downstream metal surfaces or on the iron sulfide film covering the metal. The corrosion inhibitors available in industry are polar substances, usually nitrogen derivatives dissolved in a solvent. These products are only slightly volatile and decompose at about 250.degree. C., thus they rapidly become concentrated by solubility into the phase consisting of liquid hydrocarbons, in such a way that they exercise their function only in the presence of the liquid hydrocarbon phase.
An object of the present invention is to extend the domain of action of the corrosion inhibitors even to areas where water condenses, to provide effective protection against corrosion of metal parts in contact with water vapor which may condense.
In one aspect an embodiment of this invention resides in a composition for inhibiting the corrosion of metals due to contact with water containing a chloride contaminant, said composition comprising a mixture of (a) a salt of a dicarboxylic acid containing from about 10 to about 50 carbon atoms and an aliphatic amine containing from about 10 to about 30 carbon atoms, and (b) a cyclic amine or a mixture of cyclic amines containing 10 or less carbon atoms.
Another embodiment of this invention is found in a process for the inhibition of corrosion of metal due to contact of said metal with water containing a chloride contaminant which comprises injecting a neutralizing agent into the upper part of a distillation column and thereafter injecting a corrosion inhibitor composition downstream of the injection point of said neutralizing agent, said inhibitor composition comprising a mixture of (a) a salt of a dicarboxylic acid containing from about 10 to about 50 carbon atoms and an aliphatic amine containing from about 10 to about 30 carbon atoms, and (b) a cyclic amine or a mixture of cyclic amines containing 10 or less carbon atoms.
The first active constituent of the composition of the present invention consists of a salt of a dicarboxylic acid and an amine.
Dicarboxylic acids containing from about 10 to about 50 carbon atoms, and preferably from about 20 to about 40 carbon atoms per molecule are suitable for the synthesis of this salt. Numerous acids answering to these characteristics are available in industry; these are generally mixtures of acids, and may contain impurities without this being a disadvantage. Acids sold under the commercial name of "VR- 1 acid" -- which are a mixture of polybasic, principally dibasic, acids and whose average molecular weight is about 750 -- are suitable; the same applies to acids sold under the commercial names "Dimer-Acids", "D-50-MEX" and "Empol 222". The latter is an acid corresponding to the following formula: ##EQU1## and its properties are the following:
______________________________________ molecular weight 600 acidity index 180-192 iodine index 80-95 neutralization index 290-310 saponification index 185-195 index of refraction at 25.degree. C. 1.4919 density at 15.5.degree. C. in rela- tion to water at 15.6.degree. C. 0.95 flash point 277.degree. C. ignition point 316.degree. C. viscosity at 100.degree. C. 100 cst ______________________________________
In addition alkyl dicarboxylic acids, of which the alkyl portion comprises at least ten carbon atoms may also be used. Suitable acids include alkyl malonic acids, alkyl succinic acids, alkyl glutaric acids, alkyl adipic acids, alkyl pimelic acids, alkyl sebaric acids, alkyl phthalic acids. Mixtures of these acids as well as dicarboxylic acids of higher molecular weight are also suitable for reaction with the hereinafter set forth aliphatic amines.
Aliphatic amines containing from about 10 to about 30, and preferably from about 12 to about 20, carbon atoms per molecule are suitable for reaction with the aforementioned acids to form the desired salt thereof. These are monoamines such as a primary amine and belong to the group consisting of decylamine, undecylamine, dodecylamine, tridecylamine, tetradecyl-, pentadecyl- hexadecyl-, heptadecyl, octadecyl-, nonadecyl-, eicosyl-, heneicosyl-, docosyl-, tricosyl-, tetracosyl-, pentacosyl-, hexacosyl- heptacosyl-, octacosyl-, nonacosyl-, triacontylamine, the corresponding alkenylamines and mixtures of these amines. These amines are prepared from the corresponding fatty acids and can be named according to the acid from which they derive: laurylamine, myristylamine, palmityl- stearyl-, arachidyl-, palmitolyl-, oleyl-, ricinoleyl-, dinoleyl-, linolenylamine, etc. Mixtures of these amines are available under commercial names such as "Alamine H26D", "Armeen HTD". These products include mixtures of alkyl amines whose alkyl portions contain principally between 16 and 18 carbon atoms and, in smaller quantities, 14 carbon atoms. Other fatty amines such as tallowamine, cocoamine, palmamine, etc. and their mixtures, as well as the hydrogenated derivatives of these amines may also be employed.
The salts of dicarboxylic acids and amines are obtained be any convenient means known in the art and, principally, by simply mixing acid and amine at room temperature, preferably with strong agitation. Higher temperatures may be employed but they should not exceed 90.degree. C. to avoid formation of amides or other undesirable products. In general, the acid and amine are used in a ratio in the range of from about 1:1 to about 3:1 equivalents of acid per equivalent of amine. One molecule of dibasic acid contains two equivalents of acid, one molecule of monoamine contains one equivalent of base.
The second active constituent of the corrosion inhibitor consists of a cyclic amine or mixture of cyclic amines with ten or less carbon atoms. As used in the present specification and appended claims the term "cyclic amine" will include cycloaliphatic amines, aromatic amines and nitrogen-containing heterocyclic compounds. For the rest of the description, this constituent will be designated as "volatile amine", for its function is precisely to be condensed last and thus follow the water condensation. The volatile amine may be chosen from the group consisting of cycloaliphatic amines, aromatic amines and nitrogen-containing heterocyclic compounds. By way of example, one may cite morpholine, cyclohexylamine, aniline, crude or refined quinoline and pyridine bases produced from coal tar extracts, etc. These latter bases have a boiling point generally between 90.degree. and 250.degree. C. and are generally carried over with water vapor. They include the following nitrogen-containing cyclic compounds:
______________________________________ pyridine (1-2%), picolines (5-10%), lutidines (10-15%), collidines (4-6%), aniline (25-30%), toluidines (10-15%), quinoline (25-30%), isoquinoline (2-3%), quinaldine (3-4%), heavy pyridines (1-2%). ______________________________________
The volatile amine of the type hereinbefore set forth and the salt of the dicarboxylic acid and amine may be present in the composition in a range of from about 1:1 to about 1:20 weight % of amine per weight % of salt. If so desired, they may be dissolved in an aliphatic alcohol or in an organic solvent such as the aromatic hydrocarbons (benzene, toluene, xylenes, ethylbenzene, diethylbenzene, cumene, etc.) paraffinic hydrocarbons (hexane, heptane, octane, nonane, decane, undecane, dodecane, etc.), as well as mixtures of hydrocarbons such as the naphthas and kerosene, may be used.
In order to be industrially useful, the corrosion inhibitor should form a film on the parts to be protected, which film will not be stripped off by fluid flow and in addition the corrosion inhibitor should also affect the quality of the hydrocarbon products especially the gasolines removed overhead in the distillation column as little as possible, consequently the inhibitor should not promote an emulsification of oil and water.